Silveria is adamant he hadn't been boozing ... telling us he suffers from insomnia and took a sleeping pill Saturday night to help him rest. When he woke up Sunday morning, David says he didn't realize he was still too tired to drive ... and accidentally rear-ended another car on the way to breakfast.

Cops arrived to the scene and put David through a standard DUI test ... but Silveria tells us they didn't detect a drop of alcohol in his system.

Silveria says he told the cops about the sleeping pill ... and that's when they made the decision to arrest him for DUI.

Silveria -- who is now a member of the band INFINIKA -- says he plans to take responsibility for his actions ... telling us, "It was an honest mistake."